The present invention is generally directed to toners, developers, and imaging processes, including a process for forming multicolor, including two-color, images, and more specifically, the present invention is directed to a process for controlling the relative humidity of colored toners by the addition thereto of colloidal silica particles surface treated or coated with a charge control additive. In one embodiment, the present invention comprises a process for effecting a reduction in the humidity sensitivity of colored, especially red, toners by adding to the toner a metal oxide, such as AEROSIL.RTM. R972, which has been treated or coated with a metal salt complex charge additive, such as bis{4-[(3',5'-dinitro-2'-hydroxybenzene)azo]-3-hydroxy-2-naphthanilide} chromate (-1) hydrogen, commercially available as AIZEN SPILON BLACK TRH.RTM., from Hodogaya Chemical, reference U.S. Pat. No. 4,433,040, the disclosure of which is totally incorporated herein by reference. The resulting toners are particularly useful in color imaging and printing systems, such as trilevel xerography. In embodiments of the present invention, the toner obtained can be utilized at a range of relative humidities of, for example, from about 10 to about 90 percent without any substantial change in its electrical characteristics in two-color imaging processes, which in an embodiment comprises charging an imaging member, creating on the member a latent image comprising areas of high, medium, and low potential, developing the low areas of potential with a developer composition, subsequently developing the high areas of potential with a developer composition, transferring the developed image to a substrate, and optionally permanently affixing the image to the substrate, reference for example copending patent application U.S. Ser. No. 706,477 (D/91110), the disclosure of which is totally incorporated herein by reference. The toner in embodiments can be comprised on resin particles, a red negatively charged pigment, a positive charge enhancing additive, such as distearyl dimethyl ammonium methyl sulfate, and on the surface thereof a component comprised of an AEROSIL.RTM. treated with a metal complex charge additive.
An advantage associated with the present invention is the ability to avoid the substantial loss of the charge level of color toners with a change in relative humidity through the use of charge control additives which when used in significant quantity lead to the deterioration of the color properties. An example of this type of charge control additive is bis{4-[(3',5'-dinitro-2'-hydroxybenzene)azo]-3-hydroxy-2-naphthanilide} chromate (-1) hydrogen (compound 1) commercially available as AIZEN SPILON BLACK TRH.RTM. from Hodogaya Chemical, which is an effective negative charge control agent, particularly for stabilizing charge with a change in humidity, but which is also a black dye, rendering it substantially unsuitable for incorporation into the bulk of colored toners through melt blending. In the bulk, this compound is typically used at loading of 3 to 5 percent by weight, while with the present invention in embodiments this additive, and similar materials have significant effects in reducing the humidity sensitivity when used at loadings of 0.03 percent. This reduction of the amount of additive used by two orders of magnitude allows the use thereof without affecting the color properties of the toner.
The humidity sensitivity of a developer is an important factor in its performance. Developers generally lose some of their charge as humidity increases. If the charge level drops to a low level, for example below 0.2 fc/.mu. as measured in a toner charge spectrograph similar to that described in U.S. Pat. No. 4,375,673, the disclosure of which is totally incorporated herein by reference, the background level will be unacceptabe. Even if the value at high humidity is not unacceptably low, changes in charge level with humidity can be very undesirable. The density developed on the photoreceptor for a given photoreceptor voltage is determined by the charge level of the toner, and a change in charge level can produce an undesirable change in the density of the image on the paper. Changes in toner charging ability can be compensated for by controlling the image voltage or toner concentration through machine control algorithms, but with added complexity. Thus, decreases in charge level up to 80 percent when changing from cold/dry to hot/wet conditions can be controlled to some extent, and usable developers can be made when the drop in charge level between extremes is 50 to 60 percent or less. In the latter situation, the control algorithms may not be able to respond immediately, leading to a temporary deterioration in image quality. Improvements in humidity sensitivity with the processes of the present invention can provide more consistent developed mass densities, and therefore, excellent optical densities over a range of relative humidities from 10 to 90 percent.
In full color copiers the cyan, magenta, and yellow toners are usually blended in well controlled ratios to obtain the desired color. The relative amount of each toner deposited on the photoreceptor and thus blended to obtain a color is strongly affected by the charge level on the toner. A small change in the charge level of any one of the cyan, magenta, or yellow can cause an undesirable shift in the final blended color unless compensated for by adjusting other machine conditions. This adds more complexity to the control conditions, and renders it even more desirable to reduce developer humidity sensitivity. Color pigments are often quite humidity sensitive, while some of the most effective charge control agents for reducing humidity sensitivity are highly colored when used at typical effective concentrations.
The present invention allows the use of colored charge control agents at concentrations of from about 0.005 to about 0.1 percent, or low enough so that they do not adversely affect the color of a developer. In embodiments, a class of colored charge control additives can reduce the drop in charge level when moving between extremes in humidity from about 50 percent to about 25 percent, thus affecting a factor of two improvement in the stability and controllability of the developer.
In a patentability search report the following United States patents are recited: U.S. Pat. No. 4,902,598 which illustrates a process for the preparation of silica based charge additives by the reaction of a tetraalkoxysilane with an alcoholic alkaline solution in the presence of a soluble charge additive, see the Abstract for example; and as background interest U.S. Pat. Nos. 3,983,045; 4,624,907; 4,680,245 and 4,985,328, the disclosures of each of these patents being totally incorporated herein by reference.
Toner compositions with colored pigments are known. For example, there is disclosed in U.S. Pat. No. 4,948,686, the disclosure of which is totally incorporated herein by reference, process for the formation of two color images with a colored developer comprised of a first toner comprised of certain resin particles, such as styrene butadiene, a first pigment such as copper phthalocyanine, a charge control additive, colloidal silica and metal salts of fatty acid external surface additives, and a first carrier comprised of a steel core with, for example, a polymethyl methacrylate overcoating containing known conductive particles of, for example, carbon black such as BLACK PEARLS.RTM. carbon black, available from Columbian Chemicals, present in an effective amount of, for example, from about 1 to about 40 weight percent of the coating, and wherein the coating weight is, for example, from about 0.2 to about 4 weight percent; and a second developer comprised of a black toner, a second charge additive and a steel core carrier with certain polymeric overcoatings, see claim 1 for example. Examples of colored toner pigments are illustrated in column 9, lines 10 to 26, and examples of charge additives for the toner are detailed in column 9, lines 27 to 43, of the aforementioned patent. For the black toner, there can be selected the components as recited in columns 10 and 11, including charge additives such as distearyl dimethyl ammonium methyl sulfate, see column 11, lines 16 to 32. More specifically, there is illustrated in the U.S. Pat. No. 4,948,686 a process for forming two-color images which comprises, for example, (1) charging an imaging member in an imaging apparatus; (2) creating on the member a latent image comprising areas of high, intermediate, and low potential; (3) developing the low areas of potential by conductive magnetic brush development with a developer comprising a colored first toner comprising a first resin present in an amount of from about 80 to about 98.8 percent by weight and selected from the group consisting of polyestes, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, and mixtures thereof; a first pigment present in an amount of from about 1 to about 15 percent by weight and selected from the group consisting of copper phthalocyanine pigments, quinacridone pigments, azo pigments, rhodamine pigments, and mixtures thereof; a charge control agent present in an amount of from about 0.2 to about 5 percent by weight; colloidal silica surface external additives present in an amount of from about 0.1 to about 2 percent by weight; external additives comprising metal salts or metal salts of fatty acids present in an amount of from about 0.1 to about 2 percent by weight; and a first carrier comprising a steel core with an average diameter of from about 25 to about 215 microns and a coating selected from the group consisting of methyl terpolymer, polymethyl methacrylate, and a blend of from about 35 to about 65 percent by weight of polymethyl methacrylate and from about 35 to about 65 percent by weight of chlorotrifluoroethylene-vinyl chloride copolymer, wherein the coating contains from 0 to about 40 percent by weight of the coating of conductive particles and wherein the coating weight is from about 0.2 to about 3 percent by weight of the carrier; ( 4) subsequently developing the high areas of potential by conductive magnetic brush development with a developer comprising a black second toner comprising a second resin present in an amount of from about 80 to about 98.8 percent by weight and selected from the group consisting of polyesters, styrene-butadiene polymers, styrene-acrylate polymers, styrene-methacrylate polymers, and mixtures thereof; a second pigment present in an amount of from about 1 to about 15 percent by weight; a second charge control additive present in an amount of from about 0.1 to about 6 percent by weight; a second carrier comprising a steel core with an average diameter of from about 25 to about 215 microns and a coating selected from the group consisting of a chlorotrifluoroethylene-vinyl chloride copolymer containing from 0 to about 40 percent by weight of conductive particles at a coating weight of from about 0.4 to about 1.5 percent by weight of the carrier; polyvinylfluoride at a coating weight of from about 0.01 to about 0.2 percent by weight of the carrier; and polyvinylchloride at a coating weight of from about 0.01 to about 0.2 percent by weight of the carrier; and (5) transferring the developed two-color image to a substrate. Imaging members suitable for use with the process of the copending application may be of any type capable of maintaining three distinct levels of potential Generally, various dielectric or photoconductive insulating material suitable for use in xerographic, ionographic, or other electrophotographic processes may be selected for the above process, and suitable photoreceptor materials include amorphous silicon, layered organic materials as disclosed in U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference, and the like. One disadvantage associated with the toners and imaging processes of the aforementioned patent include the use of a positive charged pigment, and a positive charge enhancing additive, resulting, it is believed, in images with lower resolutions than that obtained with the invention of the present application in embodiments.
Processes for obtaining electrophotographic, including xerographic, and two-colored images are known, reference for example the following U.S. Pat. No. 4,264,185, the disclosure of which is totally incorporated herein by reference, there is illustrated an apparatus for forming two color images by forming a bipolar electrostatic image of a two-color original document on a photoconductive drum; U.S. Pat. No. 4,308,821 discloses a method and apparatus for forming two-color images which employs two magnetic brushes; U.S. Pat. No. 4,378,415, the disclosure of which is totally incorporated herein by reference, illustrates a method of highlight color imaging which comprises providing a layered organic photoreceptor having a red sensitive layer and a short wavelength sensitive layer, subjecting the imaging member to negative charges, followed by subjecting the imaging member to positive charges, imagewise exposing the member, and developing with a colored developer composition comprising positively charged toner components, negatively charged toner components and carrier particles; U.S. Pat. No. 4,430,402, discloses a two-component type dry developer for use in dichromatic electrophotography which comprises two kinds of developers, each of which is comprised of a toner and a carrier; U.S. Pat. No. 4,594,302 discloses a developing process for two-colored electrophotography which comprises charging the surface of a photoreceptor with two photosensitive layers of different spectral sensitivities with one polarity, subsequently charging the photoreceptor with a different polarity, exposing a two-colored original to form electrostatic latent images having different polarities corresponding to the two-colored original, developing one latent image with a first color toner of one polarity, exposing the photoreceptor to eliminate electric charges with the same polarity as the first color toner which are induced on the surface of the photoreceptor in the vicinity of the latent image developed by the first color toner, and developing the other latent image with a second color toner charged with a polarity different from that of the first color toner; U.S. Pat. No. 4,500,616 discloses a method of developing electrostatic latent images by selectively extracting colored grains of one polarity from a mixture thereof having opposite polarity to each other in the presence of an alternating field, followed by development of the electrostatic image by the selectively extracted colored grains; U.S. Pat. No. 4,524,117 discloses an electrophotographic method for forming two-colored images which comprises uniformly charging the surface of a photoreceptor having a conductive surface and a photoconductive layer sensitive to a first color formed on the conductive substance, followed by exposing a two-colored original to form on the photoconductive layer a latent image corresponding to a second color region in the original with the same polarity as the electric charges on the surface of the photoconductive layer; U.S. Pat. No. 4,525,447, the disclosure of which is totally incorporated herein by reference, illustrated an image forming method which comprises forming on a photosensitive member an electrostatic latent image having at least three different levels of potentials, or comprising first and second latent images and developing the first and second latent images with a three component developer; U.S. Pat. No. 4,539,281 discloses a method of forming dichromatic copy images by forming an electrostatic latent image having a first image portion and a second image portion, and wherein the first image portion is developed by a first magnetic brush with a magnetic toner of a first color that is chargeable to a specific polarity, and the second image portion is developed by a second magnetic brush with a mixture of a magnetic carrier substantially not chargeable with the magnetic toner and a nonmagnetic toner of a second color chargeable to a polarity opposite to that of the magnetic toner by contact with the magnetic carrier; U.S. Pat. No. 4,562,129, the disclosure of which is totally incorporated herein by reference, illustrates a method of forming dichromatic copy images with a developer composed of a high-resistivity magnetic carrier and a nonmagnetic insulating toner, which are triboelectrically chargeable; an electrostatic latent image having at least three different levels of potential is formed and the toner and carrier are adhered, respectively, onto the first and second image portions; and U.S. Pat. No. 4,640,883, the disclosure of which is totally incorporated herein by reference, illustrates a method of forming composite or dichromatic images which comprises forming on an imaging member electrostatic latent images having at least three different potential levels, the first and second latent images being represented, respectively, by a first potential and a second potential relative to a common background potential.
The process of charging a photoresponsive imaging member to a single polarity and creating on it an image of at least three different levels, trilevel, of potential of the same polarity is described in U.S. Pat. No. 4,078,929, the disclosure of which is totally incorporated herein by reference. This patent discloses a method of creating two colored images by creating on an imaging surface a charge pattern including an area of first charge as a background area, a second area of greater voltage than the first area, and a third area of lesser voltage than the first area with the second and third areas functioning as image areas. The charge pattern is developed in a first step with positively charged toner particles of a first color and, in a subsequent development step, developed with negatively charged toner particles of a second color. Alternatively, charge patterns may be developed with a dry developer containing toners of two different colors in a single development step. According to the teachings of this patent, however, the images produced are of inferior quality compared to those developed in two successive development steps. Also of interest with respect to the trilevel process for generating images is U.S. Pat. No. 4,686,163, the disclosure of which is totally incorporated herein by reference. The aforementioned processes may be selected with the toners obtained with the process of the present invention.
The photoresponsive imaging member can be negatively charged, positively charged, or both, and the latent image formed on the surface may be comprised of either a positive or a negative potential, or both. In one embodiment, the image comprises three distinct levels of potential, all being of the same polarity. The levels of potential should be well differentiated, such that they are separated by at least 100 volts, and preferably 200 volts or more. For example, a latent image on an imaging member can comprise areas of potential at -800, -400, and -100 volts. In addition, the levels of potential may comprise ranges of potential. For example, a latent image may be comprised of a high level of potential ranging from about -500 to about -800 volts, an intermediate level of potential of about -400 volts, and a low level ranging from about -100 to about -300 volts. An image having levels of potential that range over a broad area may be created such that gray areas of one color are developed in the high range and gray areas of another color are developed in the low range with 100 volts of potential separating the high and low ranges and constituting the intermediate, undeveloped range. In this situation, from 0 to about 100 volts may separate the high level of potential from the intermediate level of potential, and from 0 to about 100 volts may separate the intermediate level of potential from the low level of potential. When a layered organic photoreceptor is employed, preferred potential ranges are from about -700 to about -850 volts for the high level of potential, from about -350 to about -450 volts for the intermediate level of potential, and from about -100 to about -180 volts for the low level of potential. These values will differ, depending upon the type of imaging member selected.
Moreover, illustrated in copending application U.S. Ser. No. 500,335/91 (D/89404), the disclosure of which is totally incorporated herein by reference, are developers, toners and imaging processes thereof. In an embodiment of the copending application, there is provided a process for forming two-color images which comprises (1) charging an imaging member in an imaging apparatus; (2) creating on the member a latent image comprising areas of high, intermediate, and low potential; (3) developing the low areas of potential by, for example, conductive magnetic brush development with a developer comprising carrier particles, and a colored first toner comprised of resin particles, colored, other than black, pigment particles, and an aluminum complex charge enhancing additive; (4) subsequently developing the high areas of potential by conductive magnetic brush development with a developer comprising a second black developer comprised of carrier particles and a toner comprised of resin, black pigment, such as carbon black, and a charge enhancing additive; (5) transferring the developed two-color image to a suitable substrate; and (6) fixing the image thereto. In an embodiment of the aforementioned copending application the first developer comprises, for example, a first toner comprised of resin present in an effective amount of from, for example, about 70 to about 98 percent by weight, which resin can be selected from the group consisting of polyesters, styrene butadiene polymers, styrene acrylate polymers, styrene methacrylate polymers, PLIOLITES.RTM., crosslinked styrene acrylates, crosslinked styrene methacrylates, and the like wherein the crosslinking component is, for example, divinyl benzene, and mixtures thereof; a first colored blue, especially PV FAST BLUE.RTM. pigment present in an effective amount of from, for example, about 1 to about 15 percent by weight, and preferably from about 5 to about 10 weight percent; an aluminum complex charge enhancing additive; and a second developer comprised of a second toner comprised of resin present in an effective amount of from, for example, about 70 to about 98 percent by weight, which resin can be selected from the group consisting of polyesters, styrene butadiene polymers, styrene acrylate polymers, styrene methacrylate polymers, PLIOLITES.RTM., crosslinked styrene acrylates, crosslinked styrene methacrylates, and the like wherein the crosslinking component is, for example, divinyl benzene, and mixtures thereof; and a black pigment present in an effective amount of from, for example, about 1 to about 15 percent by weight, and preferably from about 1 to about 5 weight percent wherein the aforementioned black toner contains a charge enhancing additive such as an alkyl pyridinium halide, and preferably cetyl pyridinium chloride, and in a preferred embodiment the black toner is comprised of 92 percent by weight of a styrene-n-butyl methylmethacrylate copolymer (58/42), 6 percent by weight of REGAL.RTM. 330 carbon black, and 2 percent by weight of the charge enhancing additive cetyl pyridinium chloride.
Illustrated in copending application U.S. Ser. No. 547,364 (D/90099), the disclosure of which is totally incorporated herein by reference, is a process for forming two-color images which comprises (1) charging an imaging member in an imaging apparatus; (2) creating on the member a latent image comprising areas of high, intermediate, and low potential; (3) developing the low areas of potential by, for example, conductive magnetic brush development with a developer comprising carrier particles, and a colored first toner comprised of resin, a positively charging pigment, and a negatively charging pigment; (4) subsequently developing the high areas of potential by conductive magnetic brush development with a developer comprising a second developer comprised of carrier particles and a toner comprised of resin, black pigment, such as carbon black, and a charge enhancing additive; (5) transferring the developed two-color image to a suitable substrate; and (6) fixing the image thereto.
Also illustrated are "Toner Processes with Metal Oxides" and "Processes for the Preparation of Composites and Toners Thereof" in copending applications U.S. Ser. No. 739,071 (D/91104) and U.S. Ser. No. 544,290 (D/90080), respectively, the disclosures of which are totally incorporated herein by reference. In U.S. Ser. No. 739,071, the use of metal oxides as toner additives avoids or minimizes scavengeless electrode contamination and in the U.S. Ser. No. 544,290 a process for preparing treated metal oxides, for example fine particle hydrophobic silicas, using a fluid bed is described.